Carb issues

Anything related to Lambrettas... ask tech questions, post helpful info, or just read and learn.
tippo88
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Wed Mar 08, 2017 3:30 am

Hopefully the last thing to sort on my LI 125 restomod which has a SR 185 kit and ScootRS PWK 28/30 carb.
If I leave the scooter overnight it won't start. If I then remove the float bowl, check that the float valve is working ( it always is) and reinstall the float bowl it then starts fairly easily.
However when it starts it won't idle, I have to keep revving it to keep it running. I've turned the idle screw all the way in to no avail.
Any help much appreciated.

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fluff34567
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Wed Mar 08, 2017 10:45 am

Fuel supply fuel starvation issue. If you have an over flow line is it clear of blockage? Is the fuel cap vent clear? And is there sufficient fuel coming out of the tank.

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dapper
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Wed Mar 08, 2017 11:42 am

There are a few mods and things to check on these carbs right from the start. Firstly, grind off the float stops in the bottom of the float bowl. Check the float height carefully. I can't be arsed to list them all, but if you do a forum search, there are plenty of photos and tips on these carbs.
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Padge
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Wed Mar 08, 2017 6:26 pm

would help if we knew what jetting/needle you're running

tippo88
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Sun Mar 26, 2017 10:39 am

Am still having issues with this. Took it to a local bike tuner who changed the jetting after which I proudly rode it home and it ran fine. However still has a problem that if left even for a couple of hrs it won't start. As before if I take the float bowl off check the main jet (always ok) and put it back then it's starts fine. 4 or 5 kicks first time then 2nd kick after that. 3 hrs later and won't start again...
I put an inline filter in place but that has made no difference. Carb has a transparent float bowl and always full of fuel.
Driving me mad !


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Padge
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Mon Mar 27, 2017 5:34 pm

as I said earlier, need to know what jets/needle you have in there

mick1
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Mon Mar 27, 2017 5:44 pm

choke might not be working correctly ?

bristolmod
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Mon Mar 27, 2017 6:01 pm

flooding when stood?

Do you always turn off your fuel tap? Does it actually work and not allow a dribble through when 'off"? Is the fuel valve in the carb working?
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tippo88
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Tue Mar 28, 2017 1:49 am

Thanks all. Main jet is 126 need to check idle and needle. Was assuming that now it runs fine and starts ok after the first time that jetting wouldn't be the issue. The fuel tap and float valve in the carb seem to work ok but I'll bounce check. One time I forgot to close the fuel tap and there was a pool of petrol on the floor , which is strange cos the float valve seems to close ok when I operate it manually

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Padge
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Tue Mar 28, 2017 7:55 am

First of all, check if choke is working properly, bin the plastic float bowl as they warp and the rubber gasket starts to leak, change it for an alloy one, as Dapper said, grind the 2 little float stops off the bottom of the new float bowl, check float height between 19-21mm (I always set them at 20) and make sure float moves freely

With these carbs the choke is not an enriching device, it adds air and fuel (not just fuel) so you need to get your pilot jet right and if it won’t start from cold (or after a few hours) and won’t tick over, it’s either excessively rich if it’s lumpy and smokes when it does start or if you rev it and it bogs and is kinda “zingy” for the first few minutes then it’s lean (which I suspect)

Jetting wise I would start with a 40 pilot, air screw 1-2 turns out, jjh needle on mid clip and your 126 main to start with, main will probably be a little large but it should a safe start

Hope that’s of some help

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